1. Field of the Invention
The invention relates generally to printers, and more particularly, to an ink jet printer having two motors, each driving one of two sets of rollers of a drive paper mechanism.
2. Related Art
Digital set-top boxes (e.g., cable television boxes, Internet terminal boxes etc.) are being used increasingly with consumer home entertainment equipment such as television sets, video cassette recorders, digital video disc (DVD) players and the like. In many cases, it may be desirable for users to obtain a hard copy of information displayed on the screen of their television sets. Specifically, users typically want to print e-mail messages, maps, recipes and information-rich content, such as still or captured scenes from live broadcasts, DVD players, movie cameras, video recorders etc.
Currently, if a user wants to have a hardcopy of the displayed information, the user has to use a conventional printer. Most conventional printers, however, are bulky, and thus require large amounts of space in users' home entertainment units. Hence, a printer specifically designed for use in home entertainment units is needed (i.e., a living room printer).
The living room printer should be of low height (i.e., low profile) and relatively narrow in width to blend in with other home entertainment equipment. In addition, since home entertainment equipment is usually stacked one atop another in home entertainment units, user access to the living room printer should preferably be through a front plane of the printer.
Designing a low profile, narrow width printer with user front plane access presents some technical difficulties. For example, some conventional ink jet printers use a two-roller paper drive mechanism. One roller (i.e., a pick roller) is used to pick print media from an input paper tray and to propel the print media to a second roller (i.e., a feed roller). The feed roller forwards the print media to a print zone where the print media is printed upon by an ink jet printhead. For ease of explanation, the channel within which the print media travels from the pick roller to the print zone will be referred to as a paper path.
The feed roller is typically placed in close proximity to the print zone. This configuration minimizes paper advance errors. Paper advance errors occur when one part of the print media (the part in the print zone) moves slower than another part of the print media (the part closest to the feed roller). One reason for this occurrence is due to a combination of print media flexibility, inertia and a friction force that develops as the print media moves along the paper path. This friction force acts in opposite direction to the direction of travel of the print media. As such, paper advance errors typically occur more frequently with increased distances between the print zone and the feed roller. Thus, placing the feed roller close to the print zone diminishes the likelihood of paper advance errors.
When a print media is skewed (i.e., when the print media is at an angle greater than zero degree in relation to the paper path) as it is picked up by the pick roller, it usually remains skewed as it reaches the print zone, thereby creating a slanted printout. In addition, both right and left margins of the print media may be offset. The extent to which the margins will be offset depends on the length of the paper path and the angle at which the print media is picked up by the pick roller.
Consequently, typical printers are designed to have a short paper path to minimize the offset of the margins of a skewed print media. However, since low-profile living room printers require front access and have stringent height requirements, a short paper path is undesirable. As such, current low-profile printers require longer paper paths, which necessitate longer gear trains to drive the rollers. A longer gear train increases the complexity of the paper drive mechanism. For example, if the teeth of one gear do not perfectly mesh with the teeth of another gear from which power is being transferred, a delay may be introduced. The delay will be equal to the elapsed time between when the motor is actuated and when the roller actually begins to move. Additional gears in the gear train equate to longer delays.
Although high precision gear trains are typically used to avoid this problem (a high precision gear train is a gear train that has the teeth of one gear that tightly interlocks with the teeth of another gear from which it receives power), they increase the complexity of assembling the paper drive mechanism of the printer which in turn increases the cost of the printer.
Therefore what is needed is a living room printer with a longer paper path that utilizes an efficient gear train. What is also needed is a printer with a gear train that has a low number of gears to transfer power from the motor to both the pick roller and the feed roller for reducing the complexity of assembling the paper drive mechanism without significantly reducing printer throughput.